Like SEO there is a lot of stuff about Adwords out there. And like SEO some is good, most is bad & out of date.
I started many years ago with Perry Marshalls book called the Definitive Guide to Adwords. It's still a good read.
Also, read Admagic's posts. He really knows the subject well.
Finally at the risk of self promotion, I also sell a course. It's currently half price to A1 members (and it has a full money back guarantee if it doesn't blow your socks off!!)